1. Field of the Invention
The present invention relates to a radio communication system, a transmitting apparatus, a radio communication control apparatus, a receiving apparatus, and a radio communication method suited to transfer asynchronous data and isochronous data among a plurality of terminals.
2. Description of the Related Art
As computers have become highly functional, it has been frequently performed that a plurality of computers are connected to form a local area network (LAN) in order to share files and data and to transfer data and electronic mail. In a conventional LAN, computers are connected by wire with the use of optical fibers, coaxial cables, or twisted pair cables.
In such a wired LAN, since connection work is required, it is difficult to form a LAN easily. In addition, cable wiring is troublesome in a wired LAN. Therefore, a radio LAN has drawn attention as a system which releases the user from wiring required for the conventional wired LAN. In this system, data collision is avoided by the use of carrier sense multiple access (CSMA) or polling when asynchronous data is transferred.
FIGS. 1A and 1B and FIGS. 2A to 2C roughly show radio data communication methods with the conventional technology. FIGS. 1A and 1B illustrate CSMA communication. Each communication apparatus formed of a personal computer and a communication unit senses whether a carrier signal is on a transfer path prior to communication. When there is no signal, the apparatus can start transmission. A communication apparatus xe2x80x9cAxe2x80x9d starts data transfer since there is not a carrier signal on the transfer path. On the other hand, since a communication apparatus xe2x80x9cBxe2x80x9d senses the carrier signal sent from the communication apparatus xe2x80x9cAxe2x80x9d on the transfer path, it does not transmit data. After a time xe2x80x9ctxe2x80x9d generated by a certain random number elapses, the communication apparatus xe2x80x9cBxe2x80x9d again senses a carrier signal. When there is no carrier signal on the path, the apparatus can transmit data. In CSMA, data may collide with each other on a transfer path. Therefore, each communication apparatus monitors a transfer path after data transfer, and if collision occurs, the data is again transmitted after a certain time period. A control station for controlling communication is not required in CSMA.
FIGS. 2A to 2C illustrate polling communication. In this method, a control station for controlling communication is provided to control communication by each communication apparatus constituting a system. The control station sequentially inquires of each communication apparatus whether it has data to be transmitted. In FIGS. 2A to 2C, a communication apparatus xe2x80x9caxe2x80x9d is inquired of first. When the communication apparatus xe2x80x9caxe2x80x9d has data to be transmitted, it transmits the data. After this transmission, the communication apparatus xe2x80x9cbxe2x80x9d is then inquired next. When it has data to be transmitted, it transmits the data. In this method, data does not collide with each other on a transfer path.
In recent years, it has been required that data, such as sound, music, and a motion picture, be transferred through such a radio LAN. Such data is usually large in size and needs to maintain continuity in time. When such data is to be transferred in the above conventional system, a data transfer rate may increase or decrease according to the increase or decrease of traffic in a transfer path.
When other data transfer is not performed and traffic is light on a transfer path, the specified transfer rate is ensured and transfer can be performed without any problems. If the traffic is heavy on the transfer path, however, a data delay becomes large and the transfer rate decreases. Therefore, to eliminate this delay, the receiving side needs to have a very large buffer. In some cases, data becomes intermittent. This means that reproduction of a motion picture or sound is paused.
Accordingly, an object of the present invention is to provide a radio communication system, a transmitting apparatus, a radio communication control apparatus, a receiving apparatus, and a radio communication method which suppress a delay time to a low level and ensure a constant transfer rate without being affected by an increase or decrease of communication traffic.
The foregoing object is achieved in one aspect of the present invention through the provision of a radio communication system including a plurality of radio communication terminals and a radio communication control terminal for controlling radio communication, including: radio communication means having transmitting means and receiving means; and radio communication control means having controlling means, transmitting means, and receiving means for controlling communication performed by the radio communication means, wherein asynchronous data and isochronous data is transferred through a radio communication path for communication among a plurality of the radio communication means.
The foregoing object is achieved in another aspect of the present invention through the provision of a radio communication method used between a plurality of radio communication terminals and a radio communication control terminal for controlling radio communication, wherein, when communication is performed among the plurality of radio communication terminals through a radio communication path, asynchronous data and isochronous data is transferred through the radio communication path.
As described above, asynchronous data and isochronous data can be transferred through a radio communication path with which communication is performed among a plurality of radio communication terminals.
The foregoing object is achieved in still another aspect of the present invention through the provision of a transmitting apparatus for transmitting information data in units of frames, including: means for requesting information-data transmission and for transmitting information related to the information data in a first time region of a frame; means for receiving information indicating whether communication according to the request is allowed and if the communication is allowed, for receiving information related to a second time region, in which communication is allowed, in the frame; and means for transmitting the information data in the second time region according to the information.
The foregoing object is achieved in yet another aspect of the present invention through the provision of a transmitting method for transmitting information data in units of frames, including the steps of: requesting information-data transmission and transmitting information related to the information data in a first time region of a frame; receiving information indicating whether communication according to the request is allowed and if the communication is allowed, receiving information related to a second time region, in which communication is allowed, in the frame; and transmitting the information data in the second time region according to the information.
As described above, since data is transferred in units of frames, a transmitting apparatus transmits a transmission request and information related to information data in a first region in a frame, and the transmitting apparatus transmits the information data in a second time region, in which communication is allowed, in the frame, the information data is transmitted at a constant transfer rate without being affected by an increase and decrease of traffic during communication.
The foregoing object is achieved in a further aspect of the present invention through the provision of a radio communication control apparatus for controlling information-data communication performed in units of frames among a plurality of radio communication terminals, including: means for receiving a transmission request of information data and for receiving information related to the information data in a first time region in a frame; determination means for determining whether transmission of the information data is allowed in a second time region in the frame, according to the received transmission request; and means for assigning the second time region to the transmission if the transmission is allowed according to the determination result of the determination means and for transmitting the assignment information, and if the transmission is not allowed, for transmitting information to that effect.
The foregoing object is achieved in a yet further aspect of the present invention through the provision of a radio communication control method for controlling information-data communication performed in units of frames among a plurality of radio communication terminals, including the steps of: receiving a transmission request of information data and receiving information related to the information data in a first time region in a frame; determining whether transmission of the information data is allowed in a second time region in the frame, according to the received transmission request; and assigning the second time region to the transmission if the transmission is allowed according to the determination result of in the determination step and transmitting the assignment information, and if the transmission is not allowed, transmitting information to that effect.
As described above, since a transmission request of information data and information related to the information data are received in a first time region in a frame, and a second time region is assigned to transmission of the information data according to these received pieces of information, control can be performed such that the information data is transmitted at a constant transfer rate without being affected by traffic during communication.
The foregoing object is achieved in a still further aspect of the present invention through the provision of a receiving apparatus for receiving information data in units of frames, including: means for receiving information related to a second time region in a frame, in which information data is transmitted, in a first time region in the frame; and means for receiving the information data according to the information related to the second time region.
The foregoing object is achieved in a yet still further aspect of the present invention through the provision of a receiving method for receiving information data in units of frames, including the steps of: receiving in a first time region of a frame information related to a second time region in the frame, in which information data is transmitted; and receiving the information data according to the information related to the second time region.
As described above, since information related to a second time region in a frame in which information data is transmitted in a first time region is received and information data is received according to the received information, the information data is received at a constant transfer rate without being affected by traffic during communication and a delay in receiving isochronous data is reduced.
According to the present invention, the radio communication control terminal for controlling information-data transfer is provided together with the radio communication terminals which transfer information data. The radio communication unit of the radio communication control terminal sets the time period required for information-data transfer by each radio communication terminal within one frame period. According to the present invention, since TDMA is performed in units of frame periods, a constant transfer rate is always ensured without being affected by an increase or decrease of communication traffic.
Since a constant transfer rate is always ensured, even when isochronous data such as motion-picture data and sound data is transferred, a delay time is suppressed to a low level and there is no need to provide a large-capacity buffer at the receiving side.
According to the present invention, since transfer can be performed with isochronous data and asynchronous data being placed together, data transfer with a higher degree of freedom is allowed.